In a conventional electronic component such as a common mode choke coil, a wire is generally wound on a core made of ferrite or the like. However, downsizing is a significant challenge also for coil components, and laminated electronic components which include a coil therein and are manufactured using ceramic lamination technology have widely been used in recent years. As an example of such a laminated electronic component, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-268455) discloses a common mode choke coil. FIG. 7 is an exploded perspective view showing the configuration of a conventional common mode choke coil 200.
The common mode choke coil 200 has a structure in which a low-magnetic-permeability portion 102 is laminated on a first magnetic material portion 101 and a second magnetic material portion 103 is laminated on the low-magnetic-permeability portion 102.
The first magnetic material portion 101 has a structure in which a plurality of magnetic material sheets 101a are laminated.
The low-magnetic-permeability portion 102 has a structure in which a plurality of low-magnetic-permeability sheets 102a are laminated and spiral coil conductors 104a, 104b, 104c, and 104d are each interposed between the two low-magnetic-permeability sheets 102a adjacent in the lamination direction. Each low-magnetic-permeability sheet 102a has a rectangular hole 102b extending therethrough in the lamination direction. In the magnetic material sheet 102a, the hole 102b is formed in a portion corresponding to the inside of the coil conductors 104a to 104d. In addition, predetermined sheets among the low-magnetic-permeability sheets 102a have via conductors 108a and 108b formed in predetermined portions for electrically connecting front and back sides.
Within the low-magnetic-permeability portion 102, the coil conductors 104a and 104b are connected to each other via the via conductor 108a to form a first coil 105a. In addition, the coil conductors 104c and 104d are connected to each other via the via conductor 108b to form a second coil 105b. Then, the first coil 105a and the second coil 105b are electromagnetically coupled to each other to constitute a common mode choke coil.
The second magnetic material portion 103 has a structure in which a plurality of magnetic material sheets 103a are laminated.
On the surface of the common mode choke coil 200, external electrodes 106a, 106b, 106c, and 106d are formed. The external electrode 106a is connected to an end of the coil conductor 104a, the external electrode 106b is connected to an end of the coil conductor 104b, the external electrode 106c is connected to an end of the coil conductor 104c, and the external electrode 106d is connected to an end of the coil conductor 104d. 
The common mode choke coil 200 having such a structure is manufactured, for example, through the following processes. First, unfired magnetic material sheets 101a, unfired low-magnetic-permeability sheets 102a, and unfired magnetic material sheets 103a are prepared. Among them, in the low-magnetic-permeability sheets 102a, the holes 102b, the via conductors 108a and 108b, and the coil conductors 104a to 104d are previously formed. A predetermined number of such magnetic material sheets 101a, a predetermined number of such low-magnetic-permeability sheets 102a, and a predetermined number of such magnetic material sheets 103a are laminated in a predetermined order and then press-bonded. The laminate formed thus is fired at a predetermined profile. Then, the external electrodes 106a to 106d are formed on the surface of the fired laminate by burning a conductive paste. In the above manner, the common mode choke coil 200 is manufactured.
When the magnetic material sheets 101a, the low-magnetic-permeability sheets 102a, and the magnetic material sheets 103a are laminated and press-bonded to form the laminate, the magnetic material sheet 101a on the lower side and the magnetic material sheet 103a on the upper side enter the holes 102b formed in the low-magnetic-permeability sheets 102a due to the pressure. In addition, the magnetic material sheet 101a on the lower side and the magnetic material sheet 103a on the upper side are connected to each other within the holes 102b. In other words, the common mode choke coil 200 has a structure in which the first magnetic material portion 101 and the second magnetic material portion 103 are connected to each other by extending in a columnar manner through the low-magnetic-permeability portion 102 present therebetween and the coil conductors 104a to 104d are arranged around the columnar magnetic materials extending through the low-magnetic-permeability portion 102.
However, the common mode choke coil 200 disclosed in Patent Document 1 has a problem that when the amounts of the magnetic material sheet 101a on the lower side and the magnetic material sheet 103a on the upper side which enter the holes 102b of the low-magnetic-permeability sheets 102a are insufficient, both sheets are not connected to each other. In other words, the common mode choke coil 200 does not have a structure in which the first magnetic material portion 101 and the second magnetic material portion 103 are connected to each other by extending through the low-magnetic-permeability portion 102 present therebetween, and thus the common mode choke coil 200 becomes defective.
As a solution to this problem, a solution of previously filling a magnetic material into the holes 102b of the low-magnetic-permeability sheets 102a is conceivable. Such a solution is disclosed, for example, in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2000-321341). Specifically, a magnetic material is previously filled into holes formed in low-magnetic-permeability sheets (nonmagnetic material sheets). Then, a coil conductor (coil pattern) is inserted between the two low-magnetic-permeability sheets adjacent in a lamination direction. A plurality of lower magnetic material sheets, a plurality of the low-magnetic-permeability sheets between which the coil conductors have been interposed, and a plurality of upper magnetic material sheets are laminated and press-bonded. The laminate formed thus is fired. As a result, a coil is formed within the laminate.
For manufacturing the coil disclosed in Patent Document 2, for example, the following method may be used to fill the magnetic material into the holes formed in the low-magnetic-permeability sheets.
First, a plurality of retaining sheets to be processed are prepared.
Next, a low-magnetic-permeability slurry, namely, a material obtained by kneading a low-magnetic-permeability material, a binder, and a solvent, is applied onto each retaining sheet with a constant thickness, thereby forming a plurality of low-magnetic-permeability sheets.
Next, a frame-shaped blade is pressed against the low-magnetic-permeability sheet on each retaining sheet and separated therefrom. Then, only a low-magnetic-permeability sheet portion corresponding to inside of the blade is removed. By so doing, a hole is formed in each low-magnetic-permeability sheet. In addition, a hole for a via conductor is also formed in some of the low-magnetic-permeability sheets.
Next, a magnetic material slurry, namely, a material obtained by kneading a magnetic material, a binder, and a solvent, is filled into the hole formed in each low-magnetic-permeability sheet. Specifically, from one principal surface side of the low-magnetic-permeability sheet, the magnetic material slurry is applied to the hole formed in the low-magnetic-permeability sheet and the periphery of the hole, thereby filling the magnetic material slurry.
In addition, a conductive paste is filled into the above-described hole for a via conductor.
Next, coil conductors having a predetermined shape are formed on surfaces of predetermined sheets among a plurality of the low-magnetic-permeability sheets by printing a conductive paste. The coil conductors may be formed prior to forming the holes in the low-magnetic-permeability sheets.
At the end, the low-magnetic-permeability sheet in which the magnetic material has been filled is peeled off from each retaining sheet.
A coil manufactured by using the low-magnetic-permeability sheets obtained through such processes has a structure in which a first magnetic material portion and a second magnetic material portion are assuredly connected to each other via a columnar magnetic material formed so as to extend through a low-magnetic-permeability portion.